1. Field of the Invention
This invention generally relates to integrated circuit (IC) and liquid crystal display (LCD) fabrication processes and, more particularly to an oxide thin film fabrication method using high-density plasma.
2. Description of the Related Art
Binary and multi-component oxides are used in numerous applications, such as electronic, optical, and electro-chemical, to exploit their micro structural, optical, and electrical properties. For example, the proper performance of IC devices depends, in part, on the characteristics of oxide gate insulator layers. Oxide film properties are dependent upon fabrication techniques, since these techniques influence bulk and interface characteristics of the film.
Currently, a number of conventional physical and chemical techniques are used for the growth or deposition of oxide thin films on substrates. For example, thin films can be grown on a suitable substrate in an oxidizing atmosphere or can be deposited directly on a substrate by transporting reactive species from a source to the substrate. For the above mentioned techniques, a critical factor controlling oxide growth or deposition and hence, the properties of the resulting oxides, is the energy state of reactive oxygen species available during processing. The bond energy of O2 is 5.1 electron-volts (eV). Therefore, to dissociate O2 molecules and selected precursors, thereby generating reactive oxygen species, a growth or deposition technique must supply an electron temperature/ion energy distribution covering the 5.1 eV noted above.
Conventional physical and chemical techniques, such as thermal oxidation or plasma enhanced chemical vapor deposition (PECVD), obtain the necessary electron temperature/ion energy distribution by providing thermal energy to the substrate and/or by creating reactive species in a plasma medium. For example, thermal oxidation obtains the necessary electron temperature/ion energy distribution by providing high thermal energy to a substrate and diffusing oxygen molecules into the substrate, thereby creating an oxide layer on the substrate surface. Thermal oxidation requires high temperatures to achieve practical growth rates. For example, temperatures of at least 800° C. are required to produce practical growth rates of silicon dioxide (SiO2) on Si substrates.
The use of temperature sensitive materials, that is, materials damaged by temperatures over 400° C., as substrates for oxide films is of increasing interest. Temperature sensitive materials include transparent materials such as glass or polymer and flexible materials such as plastic. Unfortunately, since thermal oxidation requires temperatures of at least 800° C., thermal oxidation is unsuitable for temperature sensitive materials. Other conventional physical and chemical techniques can grow or deposit oxides at temperatures below 400° C., hereafter referred to as low temperatures, by properly choosing precursors and energy sources. Unfortunately, conventional plasma based physical and chemical techniques do not control plasma energy and density independently. Thus, these conventional techniques have limited control of film growth and deposition kinetics. Consequently, the bulk and interfacial properties of the deposited films are degraded. In addition, typical low temperature deposition rates are not economically feasible.
FIG. 1 is a schematic drawing of a PECVD system (prior art). Unfortunately, modifying low temperature PECVD process parameters to increase deposition rates further reduces the quality of the bulk and interface characteristics for the resulting oxide. The system shown in FIG. 1 can be used to illustrate this point. The system in FIG. 1 uses capacitively coupled plasma. That is, high frequency power is directly connected to the top electrode and capacitively coupled to the bottom electrode. Since the two electrodes are coupled, it is not possible to independently control energy directed to the top and bottom electrodes. Unfortunately, this lack of energy control results in the reduction of quality for the resulting oxide. For example, increasing the high frequency power to accelerate the oxide growth rate leads to an increase in sheath potential, adversely affecting bulk and interface properties for the resulting oxide.
It would be advantageous if a low temperature deposition or growth process could form binary or multi-component oxide layers with bulk and interface characteristics superior to binary and multi-component oxide layers formed by conventional low temperature methods such as PECVD.
It would be advantageous if a low temperature deposition or growth process could form binary or multi-component oxide layers with bulk and interface characteristics approaching those for thermal oxide.
It would be advantageous if a low temperature deposition or growth process could deposit binary or multi-component oxide at rates greater than those for conventional low temperature methods such as PECVD.
It would be advantageous if a low temperature deposition or growth process could independently control plasma energy and density to improve bulk and interfacial properties for resulting binary and multi-component oxide thin films.